(1) Field of the Invention
This invention is in the field of cased telescoped ammunition rounds, and more particularly relates to improvements to the cartridge cases of such rounds to facilitate removal of the fired cartridge cases from the chambers of guns, particularly those having a high rate of fire.
(2) Description of Related Art
Cased telescoped ammunition in which the projectile is completely enclosed, or telescoped, within the cartridge case, reduces the volume and weight of gun systems firing such ammunition compared with the weight and volume of gun systems using conventionally shaped ammunition rounds having an equivalent rate of fire. The reduced weight and volume for equivalent fire power makes such gun systems particularly desirable for mounting in aircraft, tanks, and other mobile combat vehicles, where a gun system includes a gun and its associated ammunition storage and feed mechanisms.
When a cased telescoped ammunition round is fired, the projectile is initially accelerated by a booster charge to close, or to obturate, the barrel of the gun before the main propellant charge is ignited. A control tube is commonly used to control the initial movement of the projectile. A booster charge is located in the control tube and is separated by the tube from the main propellant charge. Products of the ignited booster charge are initially confined within the control tube by a booster piston attached to the base of the projectile. Main charge ignition does not occur until the advancing piston clears the tube, or exposes or unblocks, ignition ports in the wall of the control tube. This permits products of the burning booster charge to ignite the main charge. Ignition of the main charge is controlled by the position of the projectile and its booster piston relative to the control tube.
The external surfaces of the cartridge case of a typical cased telescoped ammunition includes a cylindrical outer casing and a front seal and a rear seal. Each such round is loaded into a cylindrical chamber of the gun from which the round is to be fired, and from which the spent cartridge case is removed, or unloaded, before another cycle of loading, firing and unloading begins. In guns from which such rounds are typically fired, the chamber housing in which a number of gun chambers may be formed can take the form of a cylinder which is rotated about its axis of symmetry similar to the rotation of the cylinder of a hand held revolver, for example. In a gun system mounted in an aircraft, the rounds are mechanically loaded into a given chamber when that chamber has a given orientation, position, or station, relative to the gun barrel. The chamber is then rotated to bring the loaded chamber into alignment with the gun barrel ready for firing. After firing, the chamber housing is again rotated to another position so that the chamber with the cartridge case of the fired round, the spent cartridge case, can be removed. Alternatively, the chamber housing may be moved linearly with respect to the gun barrel to position a chamber at a loading station where a round can be loaded into the chamber, the chamber housing is then moved to align the loaded chamber with the gun barrel. When the round is fired, the chamber housing is moved so that the chamber with the spent cartridge case is at its unloading station where the spent cartridge case is removed prepatory to another round being loaded into it. In such a gun, the loading and unloading stations for a given chamber may be the same. Cased telescoped ammunition obviously can also be fired from more conventionally operating guns firing projectiles of from 20 to 45 mm. for example.
When the interior of the cartridge case is pressurized by the burning of the propellant within the cartridge, the outer skin, or outer casing, serves to contain the propellant and to locate the end seals within the chamber so that the lips of the seals will properly seal the ends of the gun chamber to prevent gun gas from escaping. The pressure created by the burning propellant forces the end seals apart until they are constrained by the breech face of the gun forming one end of the chamber and by the the barrel face of the gun barrel which forms the other end of the chamber. This pressure also forces the outer casing, or skin, of the cartridge case radially outward into intimate contact with the inner cylindrical surface of the chamber. After such contact has been achieved, the pressure produced by the burning propellant acts to elastically deform the chamber housing, enlarging the diameter of the chamber and forcing apart the breech face and the barrel face of the gun. When the pressure within the cartridge case is relieved by the exit of the projectile from the muzzle of the gun barrel, the gun and chamber housing revert to their unpressurized dimensions. However, changes in the dimensions of the cartridge case experienced during firing cause plastic deformation, or nonelastic changes in the dimension of the cartridge case, particularly when the cartridge case is fabricated of material having a relatively low yield strength such a low carbon steel, so that the dimensions of the cartridge case do not return to their initial values.
To extract a spent cartridge case after it has been fired, it is necessary in guns with movable chamber housings to move the chamber housing so that the chamber in which the spent cartridge case is located is at its unloading position, or station. For such movement to take place as quickly as possible while requiring the minimum amount of force to accomplish such movement, it is necessary that there be sufficient clearance between the end seals of the spent cartridge case and the breech face and the barrel face of the gun to minimize any mechanical resistance to the movement of the chamber housing. To quickly and easily remove the spent cartridge case from the chamber, it is important that the outer casing not press against the inner cylindrical surface of the gun chamber, and that the spent cartridge case be sufficiently intact so that all components of the spent cartridge case can be removed together, or as an entity.
Because the elastic deformation of the typical gun firing cased telescoped ammunition is so large that it exceeds the yield strength of lower cost materials from which it is economically desirable that such cartridge cases be fabricated, there is a need for an improved cartridge case for cased telescoped ammunition rounds that provides adequate and proper clearance between the end seals and the breech and barrel faces of the gun after the round has been fired as well as between the outer casing of the cartridge case and the surface of the chamber in the chamber housing while maintaining the integrity of the spent cartridge case to facilitate its removal, and in which the use of more expensive materials is minimized to minimize the cost of manufacturing such rounds.
To reduce the pressure exerted by the outer casing of the cartridge case of a telescoped ammunition round against the surface of the chamber after the round is fired; and, thus the force needed to remove the spent cartridge case the outer casing, is typically split longitudinally or is designed so to split when fired. Such splitting prevents any pressure being exerted by the outer casing against the inner surface of the chamber when the chamber returns to its initial dimensions. In such rounds the end seals move relative the the outer casing to accommodate changes in the distance between the breech and barrel faces of the gun, which requires special means to maintain the integrity of the cartridge case so that all components of the spent cartridge case can be removed as a single entity. Typically, the joint between the end seals and the outer casing includes a sealant to prevent moisture and contaminants from entering the round, but such joints are not strong enough to maintain the integrity of a spent cartridge case with the degree of reliability required so that the problem of removing a spent prior art cartridge case as a single entity quickly, and completely with a minimum amount of energy was not consistently achieved.